Semi-submersible with triangular columns

ABSTRACT

According to the invention a semi-submersible vessel including a semi-submersible platform body is provided. The semi-submersible platform body is adapted to float in a body of water wherein the platform body comprising a plurality of pontoons arranged together to form a triangular structure, a plurality of columns having a lower portion and an upper portion, the columns extending outwardly from each corner of the triangular structure, wherein each column is triangular. Further, the semi-submersible vessel includes a deck supported by the upper portion of the columns.

FIELD

Embodiments of the present invention relate generally to semi-submersibles and more particularly to a platform body of the semi-submersibles with triangular columns.

BACKGROUND

Semi-submersible offshore platforms are frequently used when drilling, producing or storing hydrocarbons, such as oil and gas, at sea. These semi-submersibles are capable of withstanding the environmental forces subjected to the platform by the wind and the sea, primarily in terms of movements and independency of direction of the environmental forces.

Generally, semi-submersible offshore platforms are used in offshore locations where the water depth exceeds about 90 m. A typical platform includes a hull structure that has sufficient buoyancy to support the equipment deck above the surface of the water. The hull typically includes one or more submersible pontoons that support a plurality of vertically upstanding columns, which in turn support the deck above the surface of the water. The size of the pontoons and the number of columns are governed by the size and weight of the deck and equipment being supported.

Typically, the pontoons are submerged below the water surface and support production or drilling platforms by the columns extending from the underwater pontoon to a level above expected wave action. The pontoons are located below the expected height of wave action to reduce the wave-induced response of the platform.

The semi-submersibles typically have a square or polygonal shaped configuration including square or polygonal pontoon and columns, which sometimes may not provide adequate stability with the water plane area. Semi-submersibles may be affected by vortex induced motions (VIM) which are motions induced due to interactions with the external fluid. Additionally, semi-submersibles may also experience heave motions that may result in a decreased global performance i.e. the semi-submersible motions may be so large that they may not provide an adequate platform for the work for which they were designed. It may be noted that large accelerations, large motions or the semi-submersible reduce the ability for the job to be done.

It is therefore desirable to provide a semi-submersible that has an improved configuration capable of reducing VIM response and further has an improved performance with respect to the heave response in a given environment.

SUMMARY

Briefly in accordance with aspects of the present invention, a semisubmersible platform body is provided. The semi-submersible platform body is adapted to float in a body of water. The platform body includes a plurality of pontoons arranged together to form a triangular structure and a plurality of columns extending outwardly from each corner of the triangular structure, wherein each column is triangular.

In accordance with another aspect of the present invention, a semi-submersible vessel is provided. The semi-submersible vessel includes a platform body adapted to float in a body of water wherein the platform body comprising a plurality of pontoons arranged together to form a triangular structure, a plurality of columns having a lower portion and an upper portion, the columns extending outwardly from each corner of the triangular structure, wherein each column is triangular. Further, the semi-submersible vessel includes a deck supported by the upper portion of the columns.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be described in greater detail with references to the accompanying figure wherein;

FIG. 1 is a schematic diagram depicting a semi-submersible vessel in accordance with aspects of the present invention;

FIG. 2 is a schematic diagram depicting a semi-submersible platform body;

FIG. 3 is a schematic diagram depicting a top view of the platform body;

FIG. 4 is a schematic diagram depicting a top view of the platform body according to another embodiment; and

FIG. 5 is a graphical illustration of heave response amplitude for a conventional semi-submersible and the semi-submersible depicted in FIG. 1, in accordance with aspects of the present invention.

DETAILED DESCRIPTION

The description of the embodiments and applications of the present invention is being done together with the accompanying drawings, which form a part hereof. The embodiments are described herein for illustrative purposes and are subject to many variations. It is understood that various omissions and substitutions of equivalents are contemplated as circumstances may suggest or render expedient, but are intended to cover the application or implementation without departing from the spirit or scope of the present invention. Further, it is to be understood that the phraseology and terminology employed herein are for the purpose of the description and should not be regarded as limiting.

The terms “a” and “an” herein do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item.

FIG. 1 depicts a schematic diagram of a semi-submersible vessel 10 according to the aspects of the present invention. The vessel 10 includes a platform body 20 including a triangular structure 30 having a plurality of columns 24, 26, 28 extending vertically upwards adapted to support a deck 50. Although the platform body 20 is triangular according to aspects of the invention, it may be noted that alternative embodiments may include other general shapes such as rectangular or polyhedral shapes.

Referring now to FIG. 2, the semi-submersible platform body 20, which may be adapted to float in a body of water, for example sea, is depicted. The semi-submersible platform body 20 may be used for storing, drilling of hydrocarbons. The platform body 20 is schematically illustrated without unnecessary details and includes a substantially triangular structure 30, which is formed by a plurality of pontoons 32, 34, 36.

Although FIG. 2 shows a triangular pontoon structure 30, alternative embodiments may include other general shapes such as rectangular or polygonal structure (not shown). In accordance with aspects of the present invention, the triangular structure 30 includes three columns 24, 26, 28 extending outwardly from the triangular structure 30. More particularly, the columns 24, 26, 28 extend vertically upwards from the corners of the triangular structure 30.

In accordance with aspects of the present invention, the columns 24, 26, 28 are triangular in shape. More particularly, the transverse cross-section of the columns 24, 26, 28 is an equilateral triangle. In the illustrated embodiment, the triangular structure 30 is an equilateral triangle formed by three pontoons 32, 32, 36 arranged together. The triangular structure 30 includes an outer perimeter and an inner perimeter such that the inner perimeter of the triangular structure defines an open recess 40, as illustrated in FIG. 1.

More particularly, each pontoon 32, 34, 36 in the triangular structure 30 has a first side 32 a, 34 a, 36 a a second side 32 b, 34 b, 36 b, an upper edge 32 c, 34 c, 36 c and a lower edge 32 d, 34 d, 36 d, wherein the first side 32 a, 34 a, 36 a and the second side 32 b, 34 b, 36 b define a width W of the pontoon. The three pontoons are arranged such that the triangular structure 30 is formed as illustrated in FIG. 1.

It may be noted, that the columns 24, 26, 28 include a lower portion 24 a, 26 a, 28 a and an upper portion 24 b, 26 b, 28 b wherein the upper portion 24 b, 26 b, 28 b is adapted to support the platform deck 50 (as shown in FIG. 1). The platform deck 50 is adapted to support equipment 52 and possibly buildings etc. (see FIG. 1)

As previously noted, each column 24, 26, 28 has three faces, a first face 24 c, 26 c, 28 c, a second face 24 d, 26 d, 28 d and a third face 24 e, 26 e, 28 e, preferably of equal length forming an equilateral triangle. The first face 24 c, 26 c, 28 c and the second face 24 d, 26 d, 28 d are subjected to current [low from the water body and third face 24 e, 26 e, 28 e perpendicular to the current flow of the water body.

In the presently contemplated configuration, the first face 24 c, 26 c, 28 c of the column is parallel to the first side 32 a and the second side 32 b of the first pontoon 32. The second face 24 d, 26 d, 28 d of the column is parallel to the first side 34 a and the second side 34 b of the second pontoon 34, and the third face 24 e, 26 e, 28 e of the column is parallel to the first side 36 a and the second side 36 b of the third pontoon 36 respectively. Furthermore, the faces of the column are rounded at the vertices at the upper portion 24 b, 26 b, 28 b of the columns 24, 26, 28.

In accordance with aspects of the present invention, the columns 24, 26, 28 are attached to the triangular structure 30 as depicted. The columns 24, 26, 28 may be attached using welding or any other technique useful in attaching the columns 24, 26, 28 to the triangular structure 30.

Turning now to FIG. 3 and FIG. 4, top views of the semi-submersible platform body 20 of FIG. 2 are depicted. In FIG. 3, the triangular columns 24, 26, 28 are arranged such that the column 24, 26, 28 covers half the width W of the pontoon. The first column 24 covering half the width of the first pontoon 32 and the second pontoon 34, the second column 26 covering half the width of the second pontoon 34 and the third pontoon 36, and the third column 28 covering half the width of the third pontoon 36 and the first pontoon 32 respectively. In another embodiment as depicted in FIG. 4, the triangular columns 24, 26, 28 may be arranged such that the columns 24, 26, 28 cover one third the width W of the pontoons. More particularly, the first column 24 covers one-third the width of the first pontoon 32 and the second pontoon 34, the second column 26 covers one third the width of the second pontoon 34 and the third pontoon 36, and the third column 28 covers one third the width of third pontoon 36 and the first pontoon 32.

It may be noted that the triangular columns 24, 26, 28 may be arranged such that they cover at least a portion of the width W of the pontoons 32, 34, 36. As previously noted, the width W of the pontoon 32, 34, 36 is the difference between the first side 32 a, 34 a, 36 a and the second side 32 b, 34 b, 36 b of the pontoon 32, 34, 36.

Referring now to FIG. 5, a graph 60 depicting heave response amplitude comparison between a conventional semi-submersible platform and the semi-submersible platform with triangular columns in accordance with the present invention is presented. As illustrated, the horizontal axis 62 in the graph represents Wave period in seconds and the vertical axis 64 represents the Heave Response in m/m. As may be noted the semi-submersible vessel 10 or a platform according to the invention when compared with the conventional semi-submersible vessel or platform of similar size displacement is found to have a better heave response. Reference numeral 66 is representative of the curve for a conventional four column semi-submersible, and reference numeral 68 is representative of a curve for a Triangular semi-submersible 10 in accordance with the present invention.

The graph 60 shows the heave response or heave motion, which may be defined as the movement of a vessel in vertical direction (Z-direction) for a given wave height, against a range of wave periods. As may be appreciated, wave energy is typically located in 10 seconds to 20 seconds range period. It is desirable to have a lower motion for the vessel during this range. As can be seen from the graph, the semi-submersible 10 according to the invention has lower heave motion when compared with the conventional semi-submersible having four columns.

As an example from the graph 60, it may be inferred that for a 1 meter wave height at 14 seconds the triangular platform will move 1 m*0.265=0.265 m (if the wave height was 2 meter then 2 times 0.265). For that same wave the conventional semi-submersible will move 1 m* 0.339 =0.339 m. Although, from the example it may seem like a small amount of movement but for wave heights around 14 meters to 17 meters, the difference between the conventional semi-submersible and the triangular semi-submersible is substantial.

Embodiments of the present invention as described hereinabove have several advantages over the conventional semi-submersibles. The configuration of the semi-submersible vessel and the platform body minimizes the water plane area which in turn results in minimizing the hull motion and further provides stability to ensure that the platform body can be used for performing the same operations as by conventional square column semi-submersibles. The present invention also minimizes drag force induced by wave motions due to the rounded edges of the triangular structure and the triangular columns.

Additionally, the equilateral triangle shape of the columns aligned with the pontoons provides good structural continuity thereby minimizing the amount of material used such as steel and provides improved constructability. Furthermore, the present invention reduces heave motions as compared to the conventional semi-submersibles.

Another advantage of the present invention is that the triangular columns reduce VIM response compared to the conventional circular, rectangular or polygonal shaped columns. The current flow around the two faces of triangular columns according to the invention does not produce vortices as in the conventional semi-submersible because the water flowing around the outside of the column does not shed vortices due to the third face of the triangular column remaining perpendicular to the current flow, which in turn does not allow the vortices to attach to the column resulting in reduction in VIM due to the inability of vortices to shed from the column's third face.

The foregoing descriptions of specific embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the present invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. The exemplary embodiment was chosen and described in order to best explain the principles of the present invention and its practical application, to thereby enable others skilled in the art to best utilize the present invention and various embodiments with various modifications as are suited to the particular use contemplated. 

1. A semi-submersible platform body adapted to float in a body of water comprising: a plurality of pontoons arranged together to form a triangular structure; and a plurality of columns extending outwardly from each corner of the triangular structure, wherein each column is triangular.
 2. The semi-submersible platform body of claim 1, wherein the triangular structure is an equilateral triangle.
 3. The semi-submersible platform body of claim 1, wherein a transverse section of each column is an equilateral triangle.
 4. The semi-submersible platform body of claim 1, wherein the triangular structure formed by the pontoons has an outer perimeter and an inner perimeter, wherein the inner perimeter defines an open recess.
 5. The semi-submersible platform body of claim 1, wherein each pontoon has a first side, a second side, an upper edge and a lower edge, wherein the first side and the second side define a width of the pontoon.
 6. The semi-submersible platform body of claim 5, wherein each face of the column is parallel to the first side and the second side of the pontoon.
 7. The semi-submersible platform body of claim 5, wherein the corners of the triangular structure are rounded along the outer perimeter.
 8. The semi-submersible platform body of claim 5, wherein the column covers half the width of the pontoon.
 9. The semi-submersible platforms body of claim 5, wherein the column covers one-third the width of the pontoon.
 10. A semi-submersible vessel, comprising: a platform body adapted to float in a body of water, the platform body comprising a plurality of pontoons arranged together to form a triangular structure; a plurality of columns having a lower portion and an upper portion, the columns extending outwardly from each corner of the triangular structure, wherein each column is triangular; and a deck supported by upper portion of the columns.
 11. The vessel according to claim 10, wherein the triangular structure is an equilateral triangle.
 12. The vessel according to claim 10, wherein a transverse section of the columns is an equilateral triangle.
 13. The vessel according to claim 10, wherein the triangular structure formed by the pontoons has an outer perimeter and an inner perimeter, wherein the inner perimeter defines an open recess.
 14. The vessel according to claim 13, wherein the corners of the triangular structure are rounded.
 15. The vessel according to claim 10, wherein each pontoon has a first side, a second side, an upper edge and a lower edge, wherein the first side and the second side define a width or the pontoon.
 16. The vessel according to claim 15, wherein each face of the column is parallel to the first side and the second side of the pontoon.
 17. The vessel according to claim 15, wherein the column covers half the width of the pontoon.
 18. The vessel according to claim 15, wherein the column covers one-third the width of the pontoon.
 19. The vessel according to claim 10, wherein the columns have rounded corners along the upper portion.
 20. The vessel according to claim 10, wherein a lower portion of the columns is coupled with the second side of the pontoons at the corners of the triangular structure. 